The overall objectives of these investigations are: a) to confirm and extend preliminary observations on a potentially useful animal model of human trachoma infection, involving repeated exposure of cynomolgus monkeys to Chlamydia trachomatis; b) to employ this model for studies of the pathogenesis of trachoma, emphasizing clinico-pathologic correlations, the extension of infection to extraocular organs, the effects of immunosuppression, and cellular and humoral immune responses to chlamydial antigens; and c) to utilize trachoma infection as a model for the study of basic mechanisms of the secretory immune system, with special emphasis on its ocular components.